Motor start up currents

[Hornbeam]

I only have 240V single phase supply into my workshop.
I currently run a 3HP 600mm bandsaw and 3HP 12 inch panel saw using VFD and have no problems
I am just looking at a Sedgewick single phase MB planer which has a 4 HP motor. Running current is no problem however start up is quoted at up to 87 Amps. They recommend a 40amp type C breaker which is no problem but I am concerned regarding the main incoming fuse which is only rated at 60 amps (neighbors property is a 100 amp fuse) . I should be able to get my fuse uprated but if I have more than a couple of KW on elsewhere in the property I could still tip over the threshold on startup Any conment welcomed
Ian

 

[RogerS]

Fear not. I ran my single phase MB from a normal blue 16A circuit without problem. I don't recall the MCB rating though but wouldn't be any larger than a 32A and certainly did nothing to the main fuse or elsewhere. Remember that this surge is only there for a very, very short time. If it was there long enough to take out a 60 A cartridge fuse then you'd be looking at getting a new motor.

 

[Hornbeam]

The older MBs are only 3Hp/2,2kW. The newer ones are 4Hp/3kw
Ian

 

[RogerS]

The older MBs are only 3Hp/2,2kW. The newer ones are 4Hp/3kw
Ian

Ah...good spot, Ian. I am confused though as the documentation that came with mine also spec'd an 87A start-up surge.

 

[HappyHacker]

A 60 Amp fuse is usually good for over 100 Amp for some time, I have not got the books handy that give the actual time. It should not trip on a short start overload even with other loads unless they are very high.

 

[Sideways]

The Household cutoff fuse or "company fuse" - will have it's type marked on the fuse carrier. Older ones were BS1361, newer ones BS88 if I remember right.
I've just googled the time / current curves for this (quicker than getting the book out) and there are lots of these charts in the public domain, just make sure you get the right type (standard) of fuse.
For a 60 Amp rated fuse, it looks to be good for 150 Amps for around 200 seconds before blowing. You might get away with 300A for 10 sec. Beware that fuses have pretty crude tolerance bands, but you should be OK.
You can ignore all the small stuff, just be cautious of using your single phase kit when there's a mixed load of oven / kettle / tumble dryer and any other kind of electric heating / water heating going on. These can add 13 Amps of load apiece for more than a couple of minutes so you could get be unlucky.
I've measured a startup spike of over 50 Amps on a 1.5kW single phase planer thicknesser before now, and that's wired through a 13A plug. The only way that fuse is surviving is if the peak is of very short duration. I'd expect the same in your case. You may very well see the 80 Amps (6-7x full load current is not unusual) but only for a moment or two.
Cheers

 

[Doug B]

Hi Hornbeam, my Hammer planer thicknesser is the same at 4hp 3kw single phase as I believe is my spindle moulder, I was told the peak amp draw was for such a short time that it wouldn’t be a problem & it hasn’t been even though the workshop fuse box is fed through a modern 63amp trip fitted onto the meter tails.
I’m surprised they say a 40amp breaker, you’ll definitely need a type C but both of my machines are on 20amp type C breakers.

 

[RickG]

As others have said, the service fuse in the system is a safeguard for the supplier really. It would do nothing at all to protect you or your power distribution wiring in the house/workshop/garage. That's why we all tend to have a distribution board, with our own protection, as close after the intake as possible.

For protection, the service fuse is about as useful as a cut-down 6" nail, but then, if it were ever to fail, it would be a PITA to get it replaced.

 

[RogerS]

.....but then, if it were ever to fail, it would be a PITA to get it replaced.

If you're talking about the fuse with the wee bit of twisted wire just before the meter then for those of us living out in the sticks with 11Kv overhead wires and a transformer on a pole rest assured that there is another fuse on the pole that is even more of a PITA to be replaced.

We used to live in an area of AONB and they undergrounded the overhead 11kv lines feeding us. Part of the operation entailed removing our fuse on the pole and storing it for safety. After several days, the project was coming to an end. The Project Manager and I were sharing a cuppa and shooting the breeze outside waiting for the moment when the fuse would be refitted. We watched the man trek across the field, look down, scratch head, look some more then pick up the mobile and make a call. The conversation went along the lines of ...

"Where do you say you put it ? Foot of the pole ? Well, I can't see it. Are you sure ?". I watched the Project Manager go pale.

"What colour is the fuse?" I asked him.
"Reddish-brown" he replied.
"What colour is Herefordshire clay soil?" I asked.
"Reddish-brown" he replied.
"They've buried it, haven't they?" I said
"Yup"

 

[Hornbeam]

Thanks for the comments. I will be replacing my fuse board later this year so will try and get main incoming fuse uprated at the same time. Cartidge/wire type fuses are generally much less sensitive than MCBs which will be fitted. Understand the time at amps as basically for a wire fuse it has to melt.
Other plus side was that I came to the conclusion I didnt like the sedgewick and will go for an machine with lift up tables. I did really like the finish and lack of noise from the spiral block. Mow looking at Hammer
Thanks again
Ian

 

[RogerS]

Thanks for the comments. I will be replacing my fuse board later this year so will try and get main incoming fuse uprated at the same time. Cartidge/wire type fuses are generally much less sensitive than MCBs which will be fitted. Understand the time at amps as basically for a wire fuse it has to melt.
Other plus side was that I came to the conclusion I didnt like the sedgewick and will go for an machine with lift up tables. I did really like the finish and lack of noise from the spiral block. Mow looking at Hammer
Thanks again
Ian

Ian, I am curious as to why you want lift-up tables ? No offence intended but I can't see any sane reason to go that route. Trust me..I lived and loved that Sedgwick for many years. Reluctantly I had to sell it when I moved as the local electricity supply at the house was iffy. I bought a Hammer combi. It has the same sort of lift up tables as what you're looking at.

Compare and contrast.

Sedgwick - going from planer to thicknesser mode. Well, you don't need to as it's already available. Just wind the table down a tad, remove the extraction hood and replace on top, adjust thicknesser table to the height you need. Will pretty much already be close depending on the size of stock you're thicknessing.

Hammer

Remove fence and find place to put it somewhere for safety.
Open tables and flip up.
Remove extraction hose and flip extraction hood up and over into thicknessing mode.
Walk the extraction hose round the machine and refit (as the hood port is now facing the other way)
Walk back round to the other side and start winding the thicknesser table up. And up. And up. And up...because you have to wind it down to at least a height of 170mm or greater so that the hood can be swung into position.
OK - start thicknessing.

Ooops...large chunk came out of the stock unexpectedly. Need to plane up another piece.
Wind thicknesser table down. And down. And down. And down.
Remove hose from hood and walk it back round to the other side.....losing the will to live here.

 

[RogerS]

Ian

I see I posted more about this here

http://thewoodhaven2.co.uk/viewtopic.ph ... 167#p52167

I'd forgotten (I'm assuming the fence is the same arrangement on all their machines) just how bad it is compared to the Sedgwick.

Hammer
0) aluminium extrusion
1) you have to remove it to go to thickness mode - at least you do on mine
2) dished
3) only fixed at one end...flops around all over the place especially at the key point ie by the block
4) refitting it never goes back to 90 degrees. Tightening pushes it out of whack
5) using it, a right old PITA

Sedgwick
0) cast iron
1) stays on the machine
2) flat
3) rock solid...needs a sledge hammer to shift it once locked
4) stays at 90 degrees
5) using it, a joy